THE INFLUENCE OF OVULATION RATE, EARLY EMBRYONIC DEATH, AND UTERINE CAPACITY ON LITTER SIZE IN SWINE

Despite extensive efforts, average litter size has improved at a very slow pace during the past 20 years. Litter size is determined by uteri ne capacity or ovulation rate minus early embryonic death, whichever v alue is smaller. Selection for just one trait, therefore, does not sub stantially increase litter size. Ovulation rate is an important compon ent that maximizes reproduction in pigs; this rate establishes the cei ling for litter size. Ovulation rate is associated with breed and incr eases with parity. Among other factors, losses may be attributed to ea rly embryonic death that occurs during the first 30 days of gestation. Early embryonic death is affected by nutrition, season, time of breed ing, and semen quality. Uterine capacity is the number of piglets that the sow can carry to term. Insufficient uterine capacity leads to fet al death after 30 days of gestation and can also result in low and var iable birth weights.